Magnetoresistance effect element and heusler alloy

ABSTRACT

Provided are magnetoresistance effect element and a Heusler alloy in which an amount of energy required to rotate magnetization can be reduced. The magnetoresistance effect element includes a first ferromagnetic layer, a second ferromagnetic layer, and a non-magnetic layer positioned between the first ferromagnetic layer and the second ferromagnetic layer, in which at least one of the first ferromagnetic layer and the second ferromagnetic layer is a Heusler alloy in which a portion of elements of an alloy represented by Co2FeαZβ is substituted with a substitution element, in which Z is one or more elements selected from the group consisting of Mn, Cr, Al, Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α&lt;β, and 0.5&lt;α&lt;1.9, and the substitution element is an element different from the Z element and has a smaller magnetic moment than Co.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a magnetoresistance effect element anda Heusler alloy.

Priority is claimed on Japanese Patent Application No. 2019-146359 filedin Japan on Aug. 8, 2019, the content of which is incorporated herein byreference.

Description of Related Art

A magnetoresistance effect element is an element whose resistance valuechanges in a lamination direction due to a magnetoresistance effect. Amagnetoresistance effect element includes two ferromagnetic layers and anon-magnetic layer sandwiched therebetween. A magnetoresistance effectelement in which a conductor is used for a non-magnetic layer is calleda giant magnetoresistance (GMR) element, and a magnetoresistance effectelement in which an insulating layer (a tunnel barrier layer, a barrierlayer) is used for a non-magnetic layer is called a tunnelmagnetoresistance (TMR) element. The magnetoresistance effect elementcan be applied in various applications such as magnetic sensors,high-frequency components, magnetic heads, and magnetic random accessmemories (MRAMs).

Non-Patent Document 1 describes an example in which aCo₂FeGa_(0.5)Ge_(0.5) alloy, which is a Heusler alloy, is used for aferromagnetic layer of the GMR element. Heusler alloys have been studiedas materials that have a high likelihood of achieving a spinpolarization of 100% at room temperature.

Non-patent Document

[Non-Patent Document 1] Appl. Phys. Lett. 108, 102408 (2016).

SUMMARY OF THE INVENTION

Storage elements using a magnetoresistance effect element (for example,an MRAM) store information by utilizing magnetization reversal of aferromagnetic layer. High-frequency devices using a magnetoresistanceeffect element oscillate a high-frequency by utilizing precessionalmotion of magnetization of a ferromagnetic layer. Magnetic sensors readan external magnetic state by utilizing rotation of magnetization oroscillation of magnetization of a ferromagnetic layer. When amagnetization direction of a ferromagnetic layer is made to be easilychanged (magnetization rotation or magnetization reversal becomes easy),an amount of energy required to drive the element decreases. A Heusleralloy has a smaller value of saturation magnetization compared to a CoFealloy or the like, and a magnetization direction of the ferromagneticlayer changes easily. There is a demand for a magnetoresistance effectelement and a Heusler alloy in which an amount of energy required torotate magnetization can be further reduced.

The present disclosure has been made in view of the above circumstances,and an objective of the present disclosure is to provide amagnetoresistance effect element and a Heusler alloy in which an amountof energy required to rotate magnetization can be further reduced.

The inventors of the present disclosure have found that an amount ofenergy required to rotate magnetization of a ferromagnetic layer can befurther reduced by substituting a portion of elements constituting aHeusler alloy with an element having a small magnetic moment. Thepresent disclosure provides the following means in order to solve theabove problems.

[1] A magnetoresistance effect element according to a first aspectincludes a first ferromagnetic layer, a second ferromagnetic layer, anda non-magnetic layer positioned between the first ferromagnetic layerand the second ferromagnetic layer, in which at least one of the firstferromagnetic layer and the second ferromagnetic layer is a Heusleralloy in which a portion of elements of an alloy represented byCo₂Fe_(α)Z_(β) is substituted with a substitution element, in which Z isone or more elements selected from the group consisting of Mn, Cr, Al,Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α<β, and 0.5<α<1.9, and thesubstitution element is an element different from the Z element and hasa smaller magnetic moment than Co.

[2] In the magnetoresistance effect element according to theabove-described aspect, the Heusler alloy may be represented by thefollowing general expression (1).(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(a)Z_(β) . . . . (1) In expression(1), X1 is the substitution element, Y1 is one or more secondsubstitution elements selected from the group consisting of elementshaving a smaller magnetic moment than Fe, and a and b satisfy 0<a<0.5and b≥0.

[3] In the magnetoresistance effect element according to theabove-described aspect, the second substitution element may be one ormore elements selected from the group consisting of elements having amelting point higher than that of Fe among elements of Groups 4 to 10.

[4] In the magnetoresistance effect element according to theabove-described aspect, the Heusler alloy may be represented by thefollowing general expression (2). (Co_(1-a)X1_(a))₂Fe_(α)Z_(β) . . . (2)In expression (2), X1 is the substitution element, and a satisfies0<a<0.5.

[5] In the magnetoresistance effect element according to theabove-described aspect, the substitution element may be one or moreelements selected from the group consisting of Ni, Cu, Zn, Ru, Rh, Pd,Ag, Cd, Ir, Pt, and Au.

[6] In the magnetoresistance effect element according to theabove-described aspect, the substitution element may be one or moreelements selected from the group consisting of Cu, Ag, and Au.

[7] In the magnetoresistance effect element according to theabove-described aspect, the Heusler alloy may be represented by thefollowing general expression (3).(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ga_(1-c)Z1_(c))_(β) . . . (3) Inexpression (3), X1 is the substitution element, Y1 is one or more secondsubstitution elements selected from the group consisting of elementshaving a smaller magnetic moment than Fe, Z1 is one or more elementsselected from the group consisting of Mn, Cr, Al, Si, Ge, and Sn, and0<a<0.5, b≥0, and 0.1≤β(1-c) are satisfied.

[8] In the magnetoresistance effect element according to theabove-described aspect, c in general expression (3) may satisfy c >0.5.

[9] In the magnetoresistance effect element according to theabove-described aspect, the Heusler alloy may be represented by thefollowing general expression (4).(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ge_(1-d)Z2_(d))_(β) . . . (4) Inexpression (4), X1 is the substitution element, Y1 is one or more secondsubstitution elements selected from the group consisting of elementshaving a smaller magnetic moment than Fe, Z2 is one or more elementsselected from the group consisting of Mn, Cr, Al, Si, Ga, and Sn, and0<a<0.5, b≥0, and 0.1≤β(1-d) are satisfied.

[10] In the magnetoresistance effect element according to theabove-described aspect, d in general expression (4) may satisfy d<0.5.

[11] In the magnetoresistance effect element according to theabove-described aspect, Z2 may be Ga.

[12] In the magnetoresistance effect element according to theabove-described aspect, α and β may satisfy 2.3≤α+β<2.66.

[13] In the magnetoresistance effect element according to theabove-described aspect, α and β may satisfy 2.45≤α+β<2.66.

[14] In the magnetoresistance effect element according to theabove-described aspect, the non-magnetic layer may be configured tocontain Ag.

[15] In the magnetoresistance effect element according to theabove-described aspect, a NiAl layer containing a NiAl alloy may beconfigured to be provided between the first ferromagnetic layer and thenon-magnetic layer and between the second ferromagnetic layer and thenon-magnetic layer.

[16] In the magnetoresistance effect element according to theabove-described aspect, a thickness t of the NiAl layer may beconfigured to be 0<t≤0.63 nm.

[17] A Heusler alloy according to a second aspect is a Heusler alloy inwhich a portion of elements of an alloy represented by Co₂Fe_(α)Z_(β) issubstituted with a substitution element, wherein Z is one or moreelements selected from the group consisting of Mn, Cr, Al, Si, Ga, Ge,and Sn, αand β satisfy 2.3≤α+βα<β, and 0.5<α<1.9, and the substitutionelement is an element different from the Z element and has a smallermagnetic moment than Co.

An amount of energy required to rotate magnetization of theferromagnetic layer can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a magnetoresistance effect elementaccording to a first embodiment.

FIG. 2A is an example of a crystal structure of a Heusler alloyrepresented by a compositional formula of X₂YZ and having an L2₁structure.

FIG. 2B is an example of a crystal structure of a Heusler alloyrepresented by a compositional formula of X₂YZ and having a B2 structurederived from the L2₁ structure.

FIG. 2C is an example of a crystal structure of a Heusler alloyrepresented by a compositional formula of X₂YZ and having an A2structure derived from the L2₁ structure.

FIG. 3 is a cross-sectional view of a magnetoresistance effect elementaccording to a second embodiment.

FIG. 4 is a cross-sectional view of a magnetoresistance effect elementaccording to a third embodiment.

FIG. 5 is a cross-sectional view of a magnetic recording deviceaccording to application example 1.

FIG. 6 is a cross-sectional view of a magnetic recording elementaccording to application example 2.

FIG. 7 is a cross-sectional view of a magnetic recording elementaccording to application example 3.

FIG. 8 is a cross-sectional view of a spin current magnetizationrotational element according to application example 4.

FIG. 9 is a cross-sectional view of a magnetic domain wall movementelement according to application example 5.

FIG. 10 is a cross-sectional view of a magnetic domain wall movementelement according to application example 6.

FIG. 11 is a cross-sectional view of a magnetic domain wall movementelement according to application example 7.

FIG. 12 is a cross-sectional view of a magnetic domain wall movementelement according to application example 8.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present embodiment will be described in detail withreference to the drawings as appropriate. In the drawings used in thefollowing description, there are cases in which characteristic portionsare appropriately enlarged for convenience of illustration so thatcharacteristics of the present embodiment can be easily understood, anddimensional proportions of respective constituent elements may bedifferent from actual ones. Materials, dimensions, and the likeillustrated in the following description are merely examples, and thepresent disclosure is not limited thereto and can be implemented withappropriate modifications within a range not changing the gist of thepresent disclosure.

First Embodiment

FIG. 1 is a cross-sectional view of the magnetoresistance effect elementaccording to a first embodiment. FIG. 1 is a cross-sectional view of themagnetoresistance effect element 101 along a lamination direction oflayers of the magnetoresistance effect element. The magnetoresistanceeffect element 101 includes underlayers 20, a first ferromagnetic layer30, a first NiAl layer 40, a non-magnetic layer 50, a second NiAl layer60, a second ferromagnetic layer 70, and a cap layer 80 on a substrate10. The non-magnetic layer 50 is positioned between the firstferromagnetic layer 30 and the second ferromagnetic layer 70. The firstNiAl layer 40 is positioned between the first ferromagnetic layer 30 andthe non-magnetic layer 50. The second NiAl layer 60 is positionedbetween the non-magnetic layer 50 and the second ferromagnetic layer 70.

(Substrate)

The substrate 10 is a portion serving as a base of the magnetoresistanceeffect element 101. It is preferable to use a highly flat material forthe substrate 10. The substrate 10 may include, for example, a metaloxide single crystal, a silicon single crystal, a silicon single crystalwith a thermal oxide film, a sapphire single crystal, a ceramic, quartz,and glass. A material contained in the substrate 10 is not particularlylimited as long as it is a material having an appropriate mechanicalstrength and is suitable for heat treatment and microfabrication. As themetal oxide single crystal, a MgO single crystal may be exemplified. Anepitaxial growth film can be easily formed on a substrate containing aMgO single crystal using, for example, a sputtering method. Amagnetoresistance effect element using the epitaxial growth filmexhibits large magnetoresistance characteristics. Types of the substrate10 differ depending on intended products. When a product is a magneticrandom access memory (MRAIVI), the substrate 10 may be, for example, aSi substrate having a circuit structure. When a product is a magnetichead, the substrate 10 may be, for example, an AlTiC substrate that iseasy to process.

(Underlayer)

The underlayers 20 are positioned between the substrate 10 and the firstferromagnetic layer 30. The underlayers 20 may include, for example, afirst underlayer 21, a second underlayer 22, and a third underlayer 23in order from a position near the substrate 10.

The first underlayer 21 is a buffer layer which alleviates a differencebetween a lattice constant of the substrate 10 and a lattice constant ofthe second underlayer 22. A material of the first underlayer 21 may beeither a conductive material or an insulating material. The material ofthe first underlayer 21 also differs depending on a material of thesubstrate 10 and a material of the second underlayer 22, but may be, forexample, a compound having a (001)-oriented NaCl structure. The compoundhaving a NaCl structure may be, for example, a nitride containing atleast one element selected from the group consisting of Ti, Zr, Nb, V,Hf, Ta, Mo, W, B, Al, and Ce, or an oxide containing at least oneelement selected from the group consisting of Mg, Al, and Ce.

The material of the first underlayer 21 may also be, for example, a(002)-oriented perovskite-based conductive oxide represented by acompositional formula of ABO₃. The perovskite-based conductive oxide maybe, for example, an oxide containing at least one element selected fromthe group consisting of Sr, Ce, Dy, La, K, Ca, Na, Pb, and Ba as thesite A and containing at least one element selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Nb, Mo, Ru, Ir, Ta, Ce, andPb as the site B.

The second underlayer 22 is a seed layer that enhances crystallineproperties of an upper layer laminated on the second underlayer 22. Thesecond underlayer 22 may contain, for example, at least one selectedfrom the group consisting of MgO, TiN, and NiTa alloys. The secondunderlayer 22 may be, for example, an alloy containing Co and Fe. Thealloy containing Co and Fe may be, for example, Co—Fe or Co—Fe—B.

The third underlayer 23 is a buffer layer which alleviates a differencebetween a lattice constant of the second underlayer 22 and a latticeconstant of the first ferromagnetic layer 30. The third underlayer 23may contain, for example, a metal element when it is used as anelectrode for causing a detection current to flow therethrough. Themetal element may be, for example, at least one selected from the groupconsisting of Ag, Au, Cu, Cr, V, Al, W, and Pt. The third underlayer 23may be a layer containing any one of a metal, an alloy, an intermetalliccompound, a metal boride, a metal carbide, a metal silicide, and a metalphosphide which have a function of generating a spin current due to aspin Hall effect when a current flows therethrough. Further, the thirdunderlayer 23 may be a layer having, for example, a (001)-orientedtetragonal crystal structure or a cubic crystal structure and containingat least one element selected from the group consisting of Al, Cr, Fe,Co, Rh, Pd, Ag, Ir, Pt, Au, Mo, and W. The third underlayer 23 may be analloy of these metal elements or a laminate of materials consisting oftwo or more types of these metal elements. The alloy of metal elementsmay include, for example, a cubic crystal based AgZn alloy, AgMg alloy,CoAl alloy, FeAl alloy, and NiAl alloy.

The underlayers 20 function as buffer layers which alleviate adifference in lattice constants between the substrate 10 and the firstferromagnetic layer 30 and enhance crystalline properties of an upperlayer formed on the underlayers 20. The first underlayer 21, the secondunderlayer 22, and third underlayer 23 may be omitted. That is, theunderlayers 20 may be omitted or may be one layer or two layers. Also,among the first underlayer 21, the second underlayer 22, and the thirdunderlayer 23, there may be layers formed of the same material. Also,the underlayers 20 are not limited to the three layers and may be fouror more.

(first Ferromagnetic Layer and Second Ferromagnetic Layer)

The first ferromagnetic layer 30 and the second ferromagnetic layer 70are magnetic materials. The first ferromagnetic layer 30 and the secondferromagnetic layer 70 each have magnetization. The magnetoresistanceeffect element 101 outputs a change in a relative angle betweenmagnetization of the first ferromagnetic layer 30 and magnetization ofthe second ferromagnetic layer 70 as a change in a resistance value.

Magnetization of the second ferromagnetic layer 70 is easier to movethan magnetization of the first ferromagnetic layer 30. When apredetermined external force is applied, a magnetization direction ofthe first ferromagnetic layer 30 does not change (is fixed) while amagnetization direction of the second ferromagnetic layer 70 changes.When the magnetization direction of the second ferromagnetic layer 70changes with respect to the magnetization direction of the firstferromagnetic layer 30, a resistance value of the magnetoresistanceeffect element 101 changes. In this case, the first ferromagnetic layer30 may be called a magnetization fixed layer, and the secondferromagnetic layer 70 may be called a magnetization free layer.Hereinafter, a case in which the first ferromagnetic layer 30 is themagnetization fixed layer and the second ferromagnetic layer 70 is themagnetization free layer will be described as an example, but thisrelationship may be reversed.

A difference in ease of movement between the magnetization of the firstferromagnetic layer 30 and the magnetization of the second ferromagneticlayer 70 when a predetermined external force is applied is caused by adifference in coercivity between the first ferromagnetic layer 30 andthe second ferromagnetic layer 70. For example, when a thickness of thesecond ferromagnetic layer 70 is made smaller than a thickness of thefirst ferromagnetic layer 30, a coercivity of the second ferromagneticlayer 70 becomes smaller than a coercivity of the first ferromagneticlayer 30. Also, for example, an antiferromagnetic layer may be providedon a surface of the first ferromagnetic layer 30 on a side opposite tothe non-magnetic layer 50 with a spacer layer interposed therebetween.The first ferromagnetic layer 30, the spacer layer, and theantiferromagnetic layer form a synthetic antiferromagnetic structure(SAF structure). The synthetic antiferromagnetic structure is formed oftwo magnetic layers sandwiching a spacer layer therebetween. When thefirst ferromagnetic layer 30 and the antiferromagnetic layer areantiferromagnetically coupled, a coercivity of the first ferromagneticlayer 30 becomes larger than that in a case without theantiferromagnetic layer. The antiferromagnetic layer may be, forexample, IrMn, PtMn, or the like. The spacer layer may contain, forexample, at least one selected from the group consisting of Ru, Ir, andRh.

The first ferromagnetic layer 30 may contain, for example, a metalselected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloycontaining one or more of these metals, or an alloy containing thesemetals and at least one element of B, C, and N. The first ferromagneticlayer 30 is preferably Co—Fe or Co—Fe—B, for example. The firstferromagnetic layer 30 may be the same Heusler alloy as the secondferromagnetic layer 70 to be described below.

The second ferromagnetic layer 70 is a Heusler alloy. A Heusler alloy isa half metal in which electrons passing through the non-magnetic layer50 have only up or down spins and which ideally exhibits a spinpolarization of 100%.

A ferromagnetic Heusler alloy represented by X₂YZ is called a fullHeusler alloy and is a typical intermetallic compound based on a bccstructure. The ferromagnetic Heusler alloy represented by X₂YZ has acrystal structure of any one of an L2₁ structure, a B2 structure, and anA2 structure. Compounds represented by the compositional formula X₂YZhave properties of becoming increasingly crystalline in the order of L2₁structure>B2 structure>A2 structure.

FIGS. 2A-2C illustrate examples of crystal structures of a Heusler alloyrepresented by the compositional formula of X₂YZ, in which FIG. 2A is acrystal of a Heusler alloy having an L2₁ structure, FIG. 2B is a B2structure derived from the L2₁ structure, and FIG. 2C is an A2 structurederived from the L2₁ structure. In the L2₁ structure, an elemententering the X site, an element entering the Y site, and an elemententering the Z site are fixed. In the B2 structure, an element enteringthe Y site and an element entering the Z site are mixed, and an elemententering the X site is fixed. In the A2 structure, an element enteringthe X site, an element entering the Y site, and an element entering theZ site are mixed.

In the Heusler alloy according to the present embodiment, α and βsatisfy 2.3≤α+β. α is the number of Fe elements when the number of Coelements is 2 in a state before substitution, and β is the number of Zelements when the number of Co elements is 2 in a state beforesubstitution. In a state after substitution, for example, α is thenumber of Fe elements when the numbers of Co elements and substitutionelements to be described below are 2, and βis the number of Z elementsto be described below when the numbers of Co elements and substitutionelements to be described below are 2. The Heusler alloy according to thepresent embodiment is out of a stoichiometric composition (α+β=2) of theHeusler alloy represented by X₂YZ illustrated in FIG. 2A. For α+β, it ispreferable that 2.3≤α+β<2.66, and particularly preferable that2.45<α+β<2.66.

In the Heusler alloy according to the present embodiment, α and βsatisfy a relationship of α<β. There are cases in which the Fe elementis substituted with an element of the X element site. The substitutionof the Fe element for the X element site is called antisite. Theantisite causes a variation in a Fermi level of the Heusler alloy. Whenthe Fermi level varies, half-metal characteristics of the Heusler alloydeteriorate, and a spin polarization thereof decreases. The decrease inspin polarization causes a decrease in a magnetoresistance (MR) ratio ofthe magnetoresistance effect element 101. For α and β it is preferablethat α<β<2×α, and particularly preferable that α<β<1.5×α. When β doesnot become too large with respect to α, disturbances in a crystalstructure of the Heusler alloy can be suppressed, and a decrease in theMR ratio of the magnetoresistance effect element 101 can be suppressed.

Also, in the Heusler alloy according to the present embodiment, αsatisfies a relationship of 0.5<α<1.9. In order to suppress theantisite, for α, it is preferable that 0.8<α<1.33, and particularlypreferable that 0.9<α<1.2.

Also, in the Heusler alloy according to the present embodiment, someelements of an alloy represented by Co₂Fe_(α)Z_(β) are substituted witha substitution element. The Z element is one or more elements selectedfrom the group consisting of Mn, Cr, Al, Si, Ga, Ge, and Sn. Thesubstitution element is substituted with any one of the Co element, theFe element, and the Z element. The substitution element is mainlysubstituted with the Co element.

The substitution element is an element different from the Z element andhas a smaller magnetic moment than Co. The substitution element may be,for example, one or more elements selected from the group consisting ofNi, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au. Even when these elementsare substituted with the Co element, a crystal structure thereof iseasily maintained. Also, the substitution element is preferably one ormore elements selected from the group consisting of Cu, Ag, and Au. Asmaller magnitude of magnetic moment of a magnetic material per atom,which is obtained according to Hund's rule, corresponds to a smallernumber of outermost shell valence electrons. When a portion of the Coelement is substituted with one or more elements selected from the groupconsisting of Cu, Ag, and Au, the number of outermost shell valenceelectrons can be decreased and a saturation magnetization can be madesmall. When a saturation magnetization of a magnetic material is small,the magnetization is easily reversed.

The Heusler alloy according to the present embodiment may be representedby, for example, the following general expression (1).

(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)Z_(β)  (1)

In expression (1), X1 is a substitution element, and Y1 is one or moresecond substitution elements selected from the group consisting ofelements having a smaller magnetic moment than Fe. a and b satisfy0<a<0.5 and b≥0. In general expression (1), α is the number of elementsof the Y site (Fe elements or the second substitution elements) when thenumber of elements of the X site (Co elements or the substitutionelements) is 2, and β is the number of Z elements when the number ofelements of the X site is 2.

The second substitution element may be the same as or different from thesubstitution element. The second substitution element is preferably oneor more elements selected from the group consisting of elements having amelting point higher than that of Fe among elements of Groups 4 to 10 inthe periodic table. When the Fe element is substituted with an elementhaving a melting point higher than that of the Fe element, a meltingpoint of the Heusler alloy can be increased. When a melting point of theHeusler alloy increases, element diffusion from the Heusler alloy intoother layers can be suppressed, and a decrease in the MR ratio of themagnetoresistance effect element 101 can be suppressed.

Also, the Heusler alloy according to the present embodiment may berepresented by, for example, the following general expression (2).

(Co_(i-a)X1_(a))₂Fe_(α)Z_(β)  (2)

In expression (2), X1 is a substitution element. a satisfies 0<a<0.5. Ingeneral expression (1), α is the number of elements of the Y site (Feelements or the second substitution elements) when the number ofelements of the X site (Co elements or the substitution elements) is 2,and β is the number of Z elements when the number of elements of the Xsite is 2. General expression (2) is one in which the Fe element ingeneral expression (1) is not substituted and corresponds to a case inwhich b =0 in general expression (1).

Also, the Heusler alloy according to the present embodiment may berepresented by, for example, the following general expression (3).

(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ga_(1-c)Z1_(c))_(β)  (3)

In expression (3), X1 is a substitution element, Y1 is a secondsubstitution element, and Z1 is one or more elements selected from thegroup consisting of Mn, Cr, Al, Si, Ge, and Sn. General expression (3)satisfies 0<a<0.5, b≥0, and 0.1<≤β(1-c). General expression (3)corresponds to a case in which a portion of the Z element in generalexpression (1) is Ga.

Ga has a low melting point and performs ordering of the crystalstructure of the Heusler alloy even at a low temperature. When thenumber of elements of the X site (Co elements or the substitutionelements) is 2, if Ga is contained in an amount of 0.1 or more, theHeusler alloy is easily ordered even at a low temperature. In theHeusler alloy of general expression (3), element diffusion ofconstituent elements thereof into other layers can be suppressed, and adecrease in the MR ratio of the magnetoresistance effect element 101 canbe suppressed. Also, an abundance ratio of the Ga element is preferablysmaller than an abundance ratio of the Z1 element. That is, it ispreferable that c>0.5 be satisfied. When too much Ga is contained in theHeusler alloy, a melting point of the Heusler alloy is lowered, and theGa diffuses into other layers.

Also, the Heusler alloy according to the present embodiment may berepresented by, for example, the following general expression (4).

(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ge_(1-d)Z2_(d))_(β)  (4)

In expression (4), X1 is a substitution element, Y1 is a secondsubstitution element, and Z2 is one or more elements selected from thegroup consisting of Mn, Cr, Al, Si, Ga, and Sn. General expression (4)satisfies 0<a<0.5, b≥0, and 0.1≤β(1-d).

Ge is a semiconductor element and has an effect of increasingresistivity of the Heusler alloy. When the Heusler alloy contains Ge, aResistance Area product (RA) of the magnetoresistance effect elementincreases. For example, a magnetic domain wall movement element to bedescribed below or the like is required to have a large RA. The Geelement is preferably contained in an amount of 0.1 or more when thenumber of elements of X site (Co elements or the substitution elements)is 2. An abundance ratio of the Ge element is preferably higher than anabundance ratio of the Z2 element. That is, it is preferable that d<0.5be satisfied. On the other hand, when the abundance ratio of the Geelement is too large, resistivity of the Heusler alloy increases andbecomes a parasitic resistance component of the magnetoresistance effectelement 101. For β(1-d), it is more preferable that 0.63<β(1-d)<1.26,and particularly preferable that 0.84<β(11d)<1.26.

Also, in general expression (4) described above, the Z2 element may beGa. In this case, general expression (4) is represented by the followinggeneral expression (5).

(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ge_(1-d)Ga_(d))_(β)  (5)

In expression (5), X1 is a substitution element, and Y1 is a secondsubstitution element. General expression (5) satisfies 0<a<0.5, b≥0,0.1≤β(1-d), and 0.1≤βd

The Heusler alloy of general expression (5) contains Ga and Ge as the Zelement. In the Heusler alloy of general expression (5), characteristicsas a half metal are enhanced due to a synergistic effect of Ga and Ge,and thus a spin polarization thereof is improved. The magnetoresistanceeffect element 101 using the Heusler alloy of general expression (5) isfurther increased in the MR ratio and the RA due to the above-describedsynergistic effect of Ga and Ge.

In general expression (5), an abundance ratio of the Ge element ispreferably higher than an abundance ratio of the Ga element. Also, it ismore preferable that general expression (5) satisfy 0.63<β(1-d)<1.26 andparticularly preferable that it satisfy 0.84<β(1-d)<1.26.

Also, in general expression (4) described above, the Z2 element may beGa and Mn. In this case, general expression (4) is represented by thefollowing general expression (6).

(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ge_(1-d)Ga_(e)Mn_(f))_(β)  (6)

In expression (5), X1 is a substitution element and Y1 is a secondsubstitution element. General expression (6) satisfies 0<a<0.5, b≥0,e+f=d>0, 0.1≤β(1-d), 0.1≤βe, and 0.1≤βf.

Mn has an effect of increasing the MR ratio of the magnetoresistanceeffect element 101 when it coexists with Ga and Ge. Even when the Mnelement is substituted with an element of the X element site, half metalcharacteristics are not easily deteriorated. In general expression (6),an abundance ratio of the Mn element is preferably higher than anabundance ratio of the Ge element. Also, an abundance ratio of the Gaelement is preferably higher than an abundance ratio of the Ge element.Specifically, it is preferable that β(1-d) satisfy 0.4<β(1-d)<0.6, βesatisfy 0.2<βe<0.4, and βf satisfy 0.38<βf<0.76. When the Heusler alloycontains Ga, Ge, and Mn, effects due to the respective elements areexhibited, and thereby the MR ratio of the magnetoresistance effectelement 101 is further increased.

In the Heusler alloy according to the present embodiment, an amount ofenergy required to rotate magnetization can be reduced. Although thereason why an amount of energy required for magnetization rotation isreduced is not clear, it is considered that an amount of energy requiredfor magnetization rotation is reduced by overlap of a plurality offactors below.

A first factor is that a composition of the Heusler alloy is out of thestoichiometric composition of α+β=2, and is 2.3≤α+β. Thereby, density ofstates of minority spins in the Fermi energy decreases, and a dampingconstant becomes small. A damping constant is a physical quantityoriginating from a spin-orbit interaction. The damping constant is alsocalled a magnetic friction coefficient or a magnetic relaxationcoefficient, and when the damping constant is small, magnetization iseasily moved (easily rotated) due to an external force such as a spintransfer torque.

A second factor is that a portion of the elements of the alloy issubstituted with a substitution element having a smaller magnetic momentthan Co. When it is substituted with a substitution element having thesmaller magnetic moment than Co, magnetic anisotropy energy becomessmaller than that of the substance before the substitution. When themagnetic anisotropy energy of the Heusler alloy becomes small,magnetization is easily reversed.

A composition of the Heusler alloy can be measured by an X-rayfluorescence (XRF) method, an inductively coupled plasma (ICP) emissionspectroscopy method, an energy dispersive X-ray spectroscopy (EDS)method, a secondary ion mass spectrometry (SIMS) method, an Augerelectron spectroscopy (AES) method, or the like.

A crystal structure of the Heusler alloy can be measured by an X-raydiffraction (XRD) method, a reflection high-energy electron diffraction(RHEED) method, or the like. For example, in a case of the XRD, when theHeusler alloy has the L2₁ structure, peaks of (200) and (111) are shown,but when the Heusler alloy has the B2 structure, a (200) peak is shownbut a (111) peak is not shown. For example, in a case of RHEED, when theHeusler alloy has the L2₁ structure, streaks of (200) and (111) areshown, but when the Heusler alloy has the B2 structure, a (200) streakis shown, but a (111) streak is not shown.

Identification of a site of the substitution element can be measuredusing an X-ray absorption spectroscopy (XAS) method, an X-ray magneticcircular dichroism (XMCD), a nuclear magnetic resonance (NMR) method, orthe like. For example, in a case of the XAS, it suffices to observe anabsorption end of Co or Fe.

The composition, the crystal structure, and the site identification maybe analyzed during (in-situ) or after fabrication of themagnetoresistance effect element 101, or may be analyzed using one inwhich only the Heusler alloy is formed on a base material. In a case ofthe latter, it is preferable that a base material formed of a materialthat does not contain elements contained in the Heusler alloy beselected and a film thickness of the Heusler alloy be set to about 2 nmto 50 nm although it depends on resolution of analytical instruments.

(First NiAl layer and second NiAl layer)

The first NiAl layer 40 and the second NiAl layer 60 are layerscontaining a NiAl alloy. The first NiAl layer 40 is a buffer layer thatalleviates lattice mismatching between the first ferromagnetic layer 30and the non-magnetic layer 50. The second NiAl layer 60 is a bufferlayer that alleviates lattice mismatching between the non-magnetic layer50 and the second ferromagnetic layer 70.

The first NiAl layer 40 and the second NiAl layer 60 each may have athickness t of, for example, 0<t≤0.63 nm. When the thickness t is toolarge, there is a likelihood of spin scattering occurring in electronsmoving from the first ferromagnetic layer 30 (the second ferromagneticlayer 70) to the second ferromagnetic layer 70 (the first ferromagneticlayer 30). When the thickness t is within the above-described range,spin scattering in the moving electrons is suppressed, latticemismatching between the first ferromagnetic layer 30 and thenon-magnetic layer 50 is reduced, and lattice mismatching between thenon-magnetic layer 50 and the second ferromagnetic layer 70 is reduced.When the lattice mismatching between the layers is reduced, the MR ratioof the magnetoresistance effect element 101 is improved.

(Non-Magnetic Layer)

The non-magnetic layer 50 is made of a non-magnetic metal. A material ofthe non-magnetic layer 50 may be, for example, Cu, Au, Ag, Al, Cr, orthe like. The non-magnetic layer 50 preferably contains one or moreelements selected from the group consisting of Cu, Au, Ag, Al, and Cr asthe main constituent element. The “main constituent element” indicatesthat a proportion occupied by Cu, Au, Ag, Al, and Cr is 50% or more inthe compositional formula. The non-magnetic layer 50 preferably containsAg, and preferably contains Ag as the main constituent element. Since Aghas a long spin diffusion length, the MR ratio of the magnetoresistanceeffect element 101 using Ag is further increased.

The non-magnetic layer 50 may have a thickness in a range of, forexample, 1 nm or more and 10 nm or less. The non-magnetic layer 50hinders magnetic coupling between the first ferromagnetic layer 30 andthe second ferromagnetic layer 70.

Also, the non-magnetic layer 50 may be an insulator or a semiconductor.The non-magnetic insulator may be, for example, a material such asAl₂O₃, SiO₂, MgO, MgAl₂O₄, or a material in which a portion of Al, Si,and Mg of the materials described above is substituted with Zn, Be, orthe like. These materials have a large band gap and are excellent ininsulating properties. When the non-magnetic layer 50 is formed of anon-magnetic insulator, the non-magnetic layer 50 is a tunnel barrierlayer. The non-magnetic semiconductor may be, for example, Si, Ge,CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂, or the like.

(Cap Layer)

The cap layer 80 is positioned on a side of the magnetoresistance effectelement 101 opposite to the substrate 10. The cap layer 80 is providedto protect the second ferromagnetic layer 70. The cap layer 80suppresses diffusion of atoms from the second ferromagnetic layer 70.Also, the cap layer 80 also contributes to crystal orientations of eachlayer of the magnetoresistance effect element 101. When the cap layer 80is provided, magnetizations of the first ferromagnetic layer 30 and thesecond ferromagnetic layer 70 are stabilized, and the MR ratio of themagnetoresistance effect element 101 can be improved.

The cap layer 80 preferably contains a material having high conductivityso that it can be used as an electrode for causing a detection currentto flow therethrough. The cap layer 80 may contain, for example, one ormore metal elements of Ru, Ag, Al, Cu, Au, Cr, Mo, Pt, W, Ta, Pd, andIr, alloys of these metal elements, or a laminate of materialsconsisting of two or more types of these metal elements.

Next, a method of manufacturing the magnetoresistance effect element 101according to the present embodiment will be described. Themagnetoresistance effect element 101 can be obtained by laminating, forexample, the underlayers 20 (the first underlayer 21, the secondunderlayer 22, and the third underlayer 23), the first ferromagneticlayer 30, the first NiAl layer 40, the non-magnetic layer 50, the secondNiAl layer 60, the second ferromagnetic layer 70, and the cap layer 80on the substrate 10 in this order. As a method for film formation ofeach layer, for example, a sputtering method, a vapor deposition method,a laser ablation method, or a molecular beam epitaxy (MBE) method can beused.

Also, the substrate 10 may be annealed after forming the underlayers 20or after laminating the second ferromagnetic layer 70. The annealingenhances crystalline properties of each layer.

The laminate formed of the first ferromagnetic layer 30, thenon-magnetic layer 50, and the second ferromagnetic layer 70constituting the magnetoresistance effect element 101 has a columnarshape. The laminate can be formed in various shapes such as a circle, asquare, a triangle, a polygon, and the like in a plan view, and can bemanufactured by a known method such as photolithography or ion beametching.

As described above, the magnetoresistance effect element 101 accordingto the present embodiment uses the above-described Heusler alloy for atleast one of the first ferromagnetic layer 30 and the secondferromagnetic layer 70. Magnetization of the above-described Heusleralloy is easily reversed, and thus a current density during operation ofthe magnetoresistance effect element 101 can be reduced.

Second Embodiment

FIG. 3 is a cross-sectional view of a magnetoresistance effect elementaccording to a second embodiment. A magnetoresistance effect element 102is different from the magnetoresistance effect element 101 illustratedin FIG. 1 in that the first NiAl layer 40 and the second NiAl layer 60are not provided. In FIG. 3, constituents the same as those in FIG. 1will be denoted by the same references, and description thereof will beomitted.

In the magnetoresistance effect element 102 of the second embodiment, atleast one of a first ferromagnetic layer 30 and a second ferromagneticlayer 70 is the Heusler alloy described above. The magnetoresistanceeffect element 102 of the second embodiment achieves the same effects asin the magnetoresistance effect element 101 of the first embodiment.Also, the magnetoresistance effect element 102 of the second embodimentdoes not include a first NiAl layer and a second NiAl layer, and thefirst ferromagnetic layer 30, a non-magnetic layer 50, and the secondferromagnetic layer 70 are in direct contact with each other. Amagnetoresistance effect is caused by a change in relative angle betweenmagnetization directions of the two ferromagnetic layers sandwiching thenon-magnetic layer therebetween. The MR ratio is improved by directlysandwiching the non-magnetic layer 50 between the first ferromagneticlayer 30 and the second ferromagnetic layer 70. Also, layers exhibitingthe magnetoresistance effect are three layers of the first ferromagneticlayer 30, the second ferromagnetic layer 70, and the non-magnetic layer50, and thus a total thickness of the magnetoresistance effect element102 is reduced. When a thickness of one magnetoresistance effect element102 is reduced, a large number of elements can be provided in a sameregion, and the element is suitable for high recording density. Also,since steps of forming the first NiAl layer 40 and the second NiAl layer60 are not required, a manufacturing process is simplified.

Third Embodiment

FIG. 4 is a cross-sectional view of a magnetoresistance effect elementaccording to a third embodiment. A magnetoresistance effect element 103is different from the magnetoresistance effect element 101 illustratedin FIG. 1 in that underlayers 20 include a fourth underlayer 24.Therefore, in FIG. 4, constituents the same as those in FIG. 1 will bedenoted by the same references, and description thereof will be omitted.

The fourth underlayer 24 is disposed between a third underlayer 23 and afirst ferromagnetic layer 30. The fourth underlayer 24 functions as aseed layer that enhances crystalline properties of the firstferromagnetic layer 30 laminated on the underlayers 20. The fourthunderlayer 24 may be, for example, an alloy containing Co and Fe. Whenthe first ferromagnetic layer 30 is a Heusler alloy, magnetizationstability in the vicinity of a laminated interface is low. On the otherhand, the alloy containing Co and Fe has high magnetization stabilityand has high lattice matching with the Heusler alloy forming the firstferromagnetic layer 30. In the magnetoresistance effect element 103 inwhich the alloy containing Co and Fe is used for the fourth underlayer24, since magnetization of the Heusler alloy forming the firstferromagnetic layer 30 is further stabilized, the MR ratio is improvedalso at room temperature. The alloy containing Co and Fe may be, forexample, Co—Fe or Co—Fe—B.

Although embodiments of the present disclosure have been described indetail with reference to the drawings, configurations, combinationsthereof, or the like in the respective embodiments are examples, andadditions, omissions, substitutions, and other changes to theconfigurations can be made within a scope not departing from the gist ofthe present disclosure.

The magnetoresistance effect elements 101, 102, and 103 according to therespective embodiments can be used for various applications. Themagnetoresistance effect elements 101, 102, and 103 according to therespective embodiments can be applied to, for example, a magnetic head,a magnetic sensor, a magnetic memory, a high-frequency filter, or thelike.

Next, application examples of the magnetoresistance effect elementaccording to the present embodiment will be described. Further, in thefollowing application examples, the magnetoresistance effect element 101of the first embodiment is used as the magnetoresistance effect element,but the magnetoresistance effect element is not limited thereto. Forexample, in the following application examples, the same effects can beobtained also when, for example, the magnetoresistance effect element102 of the second embodiment and the magnetoresistance effect element103 of the third embodiment are used.

FIG. 5 is a cross-sectional view of a magnetic recording deviceaccording to application example 1. FIG. 5 is a cross-sectional view ofthe magnetoresistance effect element 101 along the lamination directionof the layers of the magnetoresistance effect element.

As illustrated in FIG. 5, a magnetic recording device 201 includes amagnetic head 210 and a magnetic recording medium W. In FIG. 5, onedirection in which the magnetic recording medium W extends is referredto as an X direction, and a direction perpendicular to the X directionis referred to as a Y direction. An XY plane is parallel to a mainsurface of the magnetic recording medium W. A direction connecting themagnetic recording medium W and the magnetic head 210 and perpendicularto the XY plane is referred to as a Z direction.

The magnetic head 210 has an air bearing surface (air bearing surface,medium facing surface) S facing a surface of the magnetic recordingmedium W. The magnetic head 210 moves in directions of arrow +X andarrow −X along the surface of the magnetic recording medium W at aposition separated by a fixed distance from the magnetic recordingmedium W. The magnetic head 210 includes the magnetoresistance effectelement 101 that acts as a magnetic sensor, and a magnetic recordingunit (not illustrated). A resistance measuring device 220 is connectedto the first ferromagnetic layer 30 and the second ferromagnetic layer70 of the magnetoresistance effect element 101.

The magnetic recording unit applies a magnetic field to a recordinglayer W1 of the magnetic recording medium W and determines amagnetization direction of the recording layer W1. That is, the magneticrecording unit performs magnetic recording on the magnetic recordingmedium W. The magnetoresistance effect element 101 reads information ofthe magnetization of the recording layer W1 written by the magneticrecording unit.

The magnetic recording medium W includes the recording layer W1 and abacking layer W2. The recording layer W1 is a portion which performsmagnetic recording, and the backing layer W2 is a magnetic path(magnetic flux passage) which recirculates a writing magnetic flux tothe magnetic head 210 again. The recording layer W1 records magneticinformation as a magnetization direction.

The second ferromagnetic layer 70 of the magnetoresistance effectelement 101 is a magnetization free layer. Therefore, the secondferromagnetic layer 70 exposed on the air bearing surface S is affectedby magnetization recorded in the facing recording layer W1 of themagnetic recording medium W. For example, in FIG. 5, a magnetizationdirection of the second ferromagnetic layer 70 is oriented in a +zdirection by being affected by magnetization of the recording layer W1oriented in the +z direction. In this case, magnetization directions ofthe first ferromagnetic layer 30 which is a magnetization fixed layerand the second ferromagnetic layer 70 are parallel to each other.

The second ferromagnetic layer 70 of the magnetic head 210 is theHeusler alloy described above, and an amount of energy required formagnetization reversal is small. Therefore, the magnetic head 210 canread the magnetization recorded in the recording layer W1 with highsensitivity.

Here, resistance when magnetization directions of the firstferromagnetic layer 30 and the second ferromagnetic layer 70 areparallel is different from resistance when magnetization directions ofthe first ferromagnetic layer 30 and the second ferromagnetic layer 70are antiparallel. Therefore, information on the magnetization of therecording layer W1 can be read as a change in resistance value bymeasuring resistances of the first ferromagnetic layer 30 and the secondferromagnetic layer 70 using the resistance measuring device 220.

A shape of the magnetoresistance effect element 101 of the magnetic head210 is not particularly limited. For example, in order to avoid aninfluence of a leakage magnetic field of the magnetic recording medium Wwith respect to the first ferromagnetic layer 30 of themagnetoresistance effect element 101, the first ferromagnetic layer 30may be installed at a position away from the magnetic recording mediumW.

FIG. 6 is a cross-sectional view of a magnetic recording elementaccording to application example 2. FIG. 6 is a cross-sectional view ofthe magnetoresistance effect element 101 along the lamination directionof the layers of the magnetoresistance effect element.

As illustrated in FIG. 6, a magnetic recording element 202 includes themagnetoresistance effect element 101, a power supply 230 and ameasurement unit 240 which are connected to the first ferromagneticlayer 30 and the second ferromagnetic layer 70 of the magnetoresistanceeffect element 101. When the third underlayer 23 of the underlayers 20has conductivity, the power supply 230 and the measurement unit 240 maybe connected to the third underlayer 23 instead of the firstferromagnetic layer 30. Also, when the cap layer 80 has conductivity,the power supply 230 and the measurement unit 240 may be connected tothe cap layer 80 instead of the second ferromagnetic layer 70. The powersupply 230 applies a potential difference to the magnetoresistanceeffect element 101 in the lamination direction. The measurement unit 240measures a resistance value of the magnetoresistance effect element 101in the lamination direction.

When a potential difference is generated between the first ferromagneticlayer 30 and the second ferromagnetic layer 70 by the power supply 230,a current flows in the lamination direction of the magnetoresistanceeffect element 101. The current is spin-polarized during passing throughthe first ferromagnetic layer 30 and becomes a spin-polarized current.The spin-polarized current reaches the second ferromagnetic layer 70 viathe non-magnetic layer 50. Magnetization of the second ferromagneticlayer 70 receives a spin transfer torque (STT) due to the spin-polarizedcurrent, and the magnetization is reversed. The second ferromagneticlayer 70 is the Heusler alloy described above, and the magnetization isreversed with a small amount of energy. When a relative angle between amagnetization direction of the first ferromagnetic layer 30 and amagnetization direction of the second ferromagnetic layer 70 changes, aresistance value of the magnetoresistance effect element 101 in thelamination direction changes. The resistance value of themagnetoresistance effect element 101 in the lamination direction is readby the measurement unit 240. That is, the magnetic recording element 202illustrated in FIG. 6 is a spin transfer torque (STT) type magneticrecording element.

FIG. 7 is a cross-sectional view of a magnetic recording elementaccording to application example 3. FIG. 7 is a cross-sectional view ofthe magnetoresistance effect element 101 along the lamination directionof the layers of the magnetoresistance effect element.

As illustrated in FIG. 7, a magnetic recording element 203 includes themagnetoresistance effect element 101, the power supply 230 connected toboth ends of the third underlayer 23 of the magnetoresistance effectelement 101, and the measurement unit 240 connected to the thirdunderlayer 23 and the second ferromagnetic layer 70. The thirdunderlayer 23 is a layer containing any one of a metal, an alloy, anintermetallic compound, a metal boride, a metal carbide, a metalsilicide, and a metal phosphide which have a function of generating aspin current due to a spin Hall effect when a current flowstherethrough. The third underlayer 23 may be, for example, a layercontaining a non-magnetic metal having an atomic number of 39 or higherhaving d electrons or f electrons in the outermost shell. Also, when thecap layer 80 has conductivity, the measurement unit 240 may be connectedto the cap layer 80 instead of the second ferromagnetic layer 70. Thepower supply 230 is connected to a first end and a second end of thethird underlayer 23. The power supply 230 applies a potential differencein an in-plane direction between one end portion (the first end) of thethird underlayer 23 and an end portion (the second end) thereof on aside opposite to the first end. The measurement unit 240 measures aresistance value of the magnetoresistance effect element 101 in thelamination direction. In the magnetoresistance effect element 101illustrated in FIG. 7, the first ferromagnetic layer 30 is amagnetization free layer and the second ferromagnetic layer 70 is amagnetization fixed layer.

When a potential difference is generated between the first end and thesecond end of the third underlayer 23 by the power supply 230, a currentflows along the third underlayer 23. When a current flows along thethird underlayer 23, a spin Hall effect occurs due to a spin-orbitinteraction. The spin Hall effect is a phenomenon in which moving spinsare bent in a direction perpendicular to a direction in which a currentflows. The spin Hall effect produces uneven distribution of spins in thethird underlayer 23 and induces a spin current in a thickness directionof the third underlayer 23. The spins are injected into the firstferromagnetic layer 30 from the third underlayer 23 by the spin current.

The spins injected into the first ferromagnetic layer 30 impart aspin-orbit torque (SOT) to magnetization of the first ferromagneticlayer 30. The first ferromagnetic layer 30 receives the spin-orbittorque (SOT), and the magnetization is reversed. The first ferromagneticlayer 30 is the Heusler alloy described above, and the magnetization isreversed with a small amount of energy. When a magnetization directionof the first ferromagnetic layer 30 and a magnetization direction of thesecond ferromagnetic layer 70 change, a resistance value of themagnetoresistance effect element 101 in the lamination directionchanges. The resistance value of the magnetoresistance effect element101 in the lamination direction is read by the measurement unit 240.That is, the magnetic recording element 203 illustrated in FIG. 7 is aspin-orbit torque (SOT) type magnetic recording element.

FIG. 8 is a cross-sectional view of a spin current magnetizationrotational element according to application example 4.

A spin current magnetization rotational element 300 is obtained byremoving the first NiAl layer 40, the non-magnetic layer 50, the secondNiAl layer 60, the second ferromagnetic layer 70, and the cap layer 80from the magnetic recording element 203 illustrated in FIG. 7. In thespin current magnetization rotational element 300, the firstferromagnetic layer 30 is the Heusler alloy represented by generalexpression (1) described above.

When a potential difference is generated between the first end and thesecond end of the third underlayer 23 by the power supply 230, a currentflows along the third underlayer 23. When a current flows along thethird underlayer 23, a spin Hall effect occurs due to a spin-orbitinteraction. The spins injected from the third underlayer 23 impart aspin-orbit torque (SOT) to magnetization of the first ferromagneticlayer 30. A magnetization direction of the first ferromagnetic layer 30changes due to the spin-orbit torque (SOT).

When a magnetization direction of the first ferromagnetic layer 30changes, polarization of reflected light changes due to a magnetic Kerreffect. Also, when a magnetization direction of the first ferromagneticlayer 30 changes, polarization of transmitted light changes due to amagnetic Faraday effect. The spin current magnetization rotationalelement 300 can be used as an optical element utilizing the magneticKerr effect or the magnetic Faraday effect.

FIG. 9 is a cross-sectional view of a magnetic domain wall movementelement (magnetic domain wall displacement type magnetic recordingelement) according to application example 5. A magnetic domain walldisplacement type magnetic recording element 400 includes a firstferromagnetic layer 401, a second ferromagnetic layer 402, anon-magnetic layer 403, a first magnetization fixed layer 404, and asecond magnetization fixed layer 405. In FIG. 9, a direction in whichthe first ferromagnetic layer 401 extends is referred to as an Xdirection, a direction perpendicular to the X direction is referred toas a Y direction, and a direction perpendicular to an XY plane isreferred to as a Z direction.

The non-magnetic layer 403 is sandwiched between the first ferromagneticlayer 401 and the second ferromagnetic layer 402 in the Z direction. Thefirst magnetization fixed layer 404 and the second magnetization fixedlayer 405 are connected to the first ferromagnetic layer 401 at aposition sandwiching the second ferromagnetic layer 402 and thenon-magnetic layer 403 in the X direction.

The first ferromagnetic layer 401 is a layer in which information can bemagnetically recorded according to a change in internal magnetic state.The first ferromagnetic layer 401 includes a first magnetic domain 401Aand a second magnetic domain 401B therein. Magnetization of the firstferromagnetic layer 401 at a position overlapping the firstmagnetization fixed layer 404 or the second magnetization fixed layer405 in the Z direction is fixed in one direction. Magnetization of thefirst ferromagnetic layer 401 at a position overlapping the firstmagnetization fixed layer 404 in the Z direction is fixed, for example,in a +Z direction, and magnetization of the first ferromagnetic layer401 at a position overlapping the second magnetization fixed layer 405in the Z direction is fixed, for example, in a −Z direction. As aresult, a magnetic domain wall DW is formed at a boundary between thefirst magnetic domain 401A and the second magnetic domain 401B. Thefirst ferromagnetic layer 401 can have the magnetic domain wall DWtherein. In the first ferromagnetic layer 401 illustrated in FIG. 9, amagnetization M_(401A), of the first magnetic domain 401A is oriented inthe +Z direction, and a magnetization M_(M401B) of the second magneticdomain 401B is oriented in the −Z direction.

The magnetic domain wall displacement type magnetic recording element400 can record data in a multi-valued or consecutive manner by aposition of the magnetic domain wall DW of the first ferromagnetic layer401. The data recorded in the first ferromagnetic layer 401 is read as achange in resistance value of the magnetic domain wall displacement typemagnetic recording element 400 when a read current is applied.

Proportions of the first magnetic domain 401A and the second magneticdomain 401B in the first ferromagnetic layer 401 change when themagnetic domain wall DW moves. A magnetization M₄₀₂ of the secondferromagnetic layer 402 may be oriented, for example, in the samedirection (parallel) as the magnetization M_(401A), of the firstmagnetic domain 401A, and in an opposite direction (antiparallel) to themagnetization M_(401B) of the second magnetic domain 401B. When themagnetic domain wall DW moves in the +X direction and an area of thefirst magnetic domain 401A in a portion overlapping the secondferromagnetic layer 402 in a plan view from the z direction increases, aresistance value of the magnetic domain wall displacement type magneticrecording element 400 decreases. In contrast, when the magnetic domainwall DW moves in the −X direction and an area of the second magneticdomain 401B in a portion overlapping the second ferromagnetic layer 402in a plan view from the Z direction increases, a resistance value of themagnetic domain wall displacement type magnetic recording element 400increases.

The magnetic domain wall DW moves when a write current is caused to flowin the x direction of the first ferromagnetic layer 401 or an externalmagnetic field is applied. For example, when a write current (forexample, a current pulse) is applied to the first ferromagnetic layer401 in the +X direction, since electrons flow in the −X direction thatis opposite to a direction of the current, the magnetic domain wall DWmoves in the −X direction. When a current flows from the first magneticdomain 401A toward the second magnetic domain 401B, electronsspin-polarized in the second magnetic domain 401B causes themagnetization M_(401A) of the first magnetic domain 401A to be reversed.When the magnetization M_(401A) of the first magnetic domain 401A isreversed, the magnetic domain wall DW moves in the −X direction.

As a material of the first ferromagnetic layer 401, for example, theHeusler alloy described above may be used. Magnetization of theabove-described Heusler alloy is easily reversed, and the magneticdomain wall DW can be moved with a small amount of energy.

Also, it is preferable that the magnetic domain wall displacement typemagnetic recording element 400 have a high MR ratio and a high RA. Whenthe MR ratio of the magnetic domain wall displacement type magneticrecording element 400 is high, a difference between a maximum value anda minimum value of the resistance value of the magnetic domain walldisplacement type magnetic recording element 400 increases, andreliability of data is improved. Also, when an RA of the magnetic domainwall displacement type magnetic recording element 400 is large, data canbe recorded more in an analog manner. The first ferromagnetic layer 401is preferably the Heusler alloy that satisfies general expression (4).

The second ferromagnetic layer 402 can use, for example, a metalselected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloycontaining one or more of these metals, an alloy containing these metalsand at least one element of B, C, and N, or the like. Specifically,Co—Fe, Co—Fe—B, and Ni—Fe can be exemplified. As a material of thesecond ferromagnetic layer 402, the Heusler alloy described above may beused.

The non-magnetic layer 403 can use a material the same as that of thenon-magnetic layer 50 described above. A material the same as that ofthe second ferromagnetic layer 402 can be used for the firstmagnetization fixed layer 404 and the second magnetization fixed layer405. The first magnetization fixed layer 404 and the secondmagnetization fixed layer 405 may have a SAF structure.

FIG. 10 is a perspective view of a magnetic domain wall movement element(magnetic strip device) according to application example 6.

As illustrated in FIG. 10, a magnetic strip device 500 includes amagnetic recording medium 510, a magnetic recording head 520, and apulse power supply 530. The magnetic recording head 520 is provided at apredetermined position above the magnetic recording medium 510. Thepulse power supply 530 is connected to the magnetic recording medium 510so that a pulse current can be applied in an in-plane direction of themagnetic recording medium 510. Further, in FIG. 10, one direction inwhich the magnetic recording medium 510 extends is referred to as an Xdirection, a direction perpendicular to the X direction is referred toas a Y direction, and a direction perpendicular to an XY plane isreferred to as a Z direction.

The magnetic recording medium 510 includes a magnetic strip 511, anunderlayer 512, and a substrate 513. The underlayer 512 is laminated onthe substrate 513, and the magnetic strip 511 is laminated on theunderlayer 512. The magnetic strip 511 is formed in a strip shape havinga length in the X direction larger than a width in the Y direction.

The magnetic strip 511 is formed of a magnetic material capable offorming a magnetic domain having a magnetization direction differentfrom that of the other portion in a part of a longitudinal direction.The magnetic strip 511 may include, for example, a first magnetic domain511A and a second magnetic domain 511B. A magnetization M_(511B) of thesecond magnetic domain 511B is oriented in a direction different from amagnetization M_(511A) of the first magnetic domain 511A. A magneticdomain wall DW is formed between the first magnetic domain 511A and thesecond magnetic domain 511B. The second magnetic domain 511B isgenerated by the magnetic recording head 520.

The magnetic strip device 500 performs data writing by changing aposition of the second magnetic domain 511B of the magnetic strip 511using a magnetic field or spin injection magnetization reversalgenerated by the magnetic recording head 520 while intermittentlyshifting and moving the magnetic domain wall DW of the magnetic strip511 by a pulse current supplied from the pulse power supply 530. Thedata written in the magnetic strip device 500 can be read by utilizing amagnetoresistance change or a magneto-optical change. When themagnetoresistance change is used, a ferromagnetic layer is provided at aposition facing the magnetic strip 511 with a non-magnetic layersandwiched therebetween. The magnetoresistance change is caused by adifference in relative angle between magnetization of the ferromagneticlayer and magnetization of the magnetic strip 511.

The Heusler alloy described above can be used as a material of themagnetic strip 511. When the magnetic strip 511 is the Heusler alloydescribed above, an amount of energy required to move the magneticdomain wall DW can be reduced. Also, when the Heusler alloy satisfyinggeneral expression (4) is used for the magnetic strip 511, an RA of themagnetic strip device 500 can be increased.

As a material of the underlayer 512, ferrite, which is an oxideinsulator, more specifically, soft ferrite is preferably used in atleast a portion thereof. As the soft ferrite, Mn—Zn ferrite, Ni—Znferrite, Mn—Ni ferrite, Ni—Zn—Co ferrite can be used. Since the softferrite has a high magnetic permeability and a magnetic flux of amagnetic field generated by the magnetic recording head 520 isconcentrated thereon, the soft ferrite can efficiently form the secondmagnetic domain 511B. A material the same as that of the substrate 10described above can be used for the substrate 513.

FIG. 11 is a perspective view of a magnetic domain wall movement element(magnetic domain wall movement type spatial light modulator) accordingto application example 7.

As illustrated in FIG. 11, a magnetic domain wall movement type spatiallight modulator 600 includes a first magnetization fixed layer 610, asecond magnetization fixed layer 620, and a light modulation layer 630.In FIG. 11, one direction in which the light modulation layer 630extends is referred to as an X direction, a direction perpendicular tothe X direction is referred to as a Y direction, and a directionperpendicular to an XY plane is referred to as a Z direction.

A magnetization M₆₁₀ of the first magnetization fixed layer 610 and amagnetization M₆₂₀ of the second magnetization fixed layer 620 areoriented in different directions. For example, the magnetization M₆₁₀ ofthe first magnetization fixed layer 610 may be oriented in a +Zdirection, and the magnetization M₆₂₀ of the second magnetization fixedlayer 620 may be oriented in a −Z direction.

The light modulation layer 630 can be divided into overlapping regions631 and 636, initial magnetic domain regions 632 and 635, and magneticdomain change regions 633 and 634.

The overlapping region 631 is a region overlapping the firstmagnetization fixed layer 610 in the Z direction, and the overlappingregion 636 is a region overlapping the second magnetization fixed layer620 in the Z direction. A magnetization M₆₃₁ of the overlapping region631 is affected by a leakage magnetic field from the first magnetizationfixed layer 610 and may be fixed, for example, in the +Z direction. Amagnetization M₆₃₆ of the overlapping region 636 is affected by aleakage magnetic field from the second magnetization fixed layer 620 andmay be fixed, for example, in the −Z direction.

The initial magnetic domain regions 632 and 635 are regions whosemagnetizations are fixed in directions different from those of theoverlapping regions 631 and 636 by being affected by leakage magneticfields from the first magnetization fixed layer 610 and the secondmagnetization fixed layer 620. A magnetization M₆₃₂ of the initialmagnetic domain region 632 is affected by a leakage magnetic field fromthe first magnetization fixed layer 610 and may be fixed, for example,in the −Z direction. A magnetization M₆₃₅ of the initial magnetic domainregion 635 is affected by a leakage magnetic field from the secondmagnetization fixed layer 620 and may be fixed, for example, in the +Zdirection.

The magnetic domain change regions 633 and 634 are regions in which themagnetic domain wall DW can move. A magnetization M₆₃₃ of the magneticdomain change region 633 and a magnetization M₆₃₄ of the magnetic domainchange region 634 are oriented in opposite directions with the magneticdomain wall DW sandwiched therebetween. The magnetization M₆₃₃ of themagnetic domain change region 633 is affected by the initial magneticdomain region 632 and may be oriented, for example, in the −Z direction.The magnetization M₆₃₄ of the magnetic domain change region 634 isaffected by a leakage magnetic field of the initial magnetic domainregion 635 and may be fixed, for example, in the +Z direction. Aboundary between the magnetic domain change region 633 and the magneticdomain change region 634 is the magnetic domain wall DW. The magneticdomain wall DW moves when a write current is caused to flow in the Xdirection of the light modulation layer 630 or an external magneticfield is applied.

The magnetic domain wall movement type spatial light modulator 600changes a position of the magnetic domain wall DW while moving themagnetic domain wall DW intermittently. Then, a light L1 is madeincident on the light modulation layer 630, and a light L2 reflected bythe light modulation layer 630 is evaluated. Polarization states of thelight L2 reflected by portions having different orientation directionsof magnetization are different. The magnetic domain wall movement typespatial light modulator 600 can be used as a video display deviceutilizing a difference in polarization state of the light L2.

As a material of the light modulation layer 630, the Heusler alloydescribed above can be used. Thereby, the magnetic domain wall DW can bemoved with a small amount of energy. Also, when the Heusler alloysatisfying general expression (4) is used for the light modulation layer630, an RA of the magnetic domain wall movement type spatial lightmodulator 600 can be increased. As a result, a position of the magneticdomain wall DW can be controlled more precisely, and a video displaywith higher definition is possible.

The same material as the above-described first magnetization fixed layer404 and the second magnetization fixed layer 405 can be used for thefirst magnetization fixed layer 610 and the second magnetization fixedlayer 620.

FIG. 12 is a perspective view of a high-frequency device according toapplication example 8.

As illustrated in FIG. 12, a high-frequency device 700 includes themagnetoresistance effect element 101, a direct current (DC) power supply701, an inductor 702, a capacitor 703, an output port 704, and wirings705 and 706.

The wiring 705 connects the magnetoresistance effect element 101 and theoutput port 704. The wiring 706 branches from the wiring 705 and reachesthe ground G via the inductor 702 and the DC power supply 701. For theDC power supply 701, the inductor 702, and the capacitor 703, known onescan be used. The inductor 702 cuts a high-frequency component of acurrent and passes an invariant component of the current. The capacitor703 passes a high-frequency component of a current and cuts an invariantcomponent of the current. The inductor 702 is disposed at a portion inwhich a flow of the high-frequency current is desired to be suppressed,and the capacitor 703 is disposed at a portion in which a flow of the DCcurrent is desired to be suppressed.

When an alternating current (AC) or an alternating magnetic field isapplied to the ferromagnetic layer included in the magnetoresistanceeffect element 101, magnetization of the second ferromagnetic layer 70performs precessional motion. Magnetization of the second ferromagneticlayer 70 oscillates strongly when a frequency of a high-frequencycurrent or a high-frequency magnetic field applied to the secondferromagnetic layer 70 is near a ferromagnetic resonance frequency ofthe second ferromagnetic layer 70, and does not oscillate as much at afrequency away from the ferromagnetic resonance frequency of the secondferromagnetic layer 70. This phenomenon is called a ferromagneticresonance phenomenon.

A resistance value of the magnetoresistance effect element 101 changesaccording to an oscillation of the magnetization of the secondferromagnetic layer 70. The DC power supply 701 applies a DC current tothe magnetoresistance effect element 101. The DC current flows in thelamination direction of the magnetoresistance effect element 101. The DCcurrent flows to the ground G through the wirings 706 and 705 and themagnetoresistance effect element 101. A potential of themagnetoresistance effect element 101 changes according to Ohm's law. Ahigh-frequency signal is output from the output port 704 according to achange in potential (change in resistance value) of themagnetoresistance effect element 101.

The second ferromagnetic layer 70 is the Heusler alloy described aboveand magnetization thereof can be caused to perform precessional motionwith a small amount of energy. Also, the above-described Heusler alloyhas a small saturation magnetization, and a Q value of thehigh-frequency device 700 is improved. The Q value is an indexindicating sharpness of local maximum characteristics of ahigh-frequency signal. As the Q value increases, a high-frequency signalwith a specific frequency is oscillated.

EXAMPLES Example 1

The magnetoresistance effect element 101 illustrated in FIG. 1 wasfabricated as below. A configuration of each layer was as follows.

Substrate 10: MgO single crystal substrate, thickness 0.5 mm

Underlayers 20: Layered structure of First under layer 21 and Secondunder layer 22 and Third under layer 23

First underlayer 21: MgO, thickness 10 nm

Second underlayer 22: CoFe, thickness 10 nm

Third underlayer 23: Ag, thickness 50 nm

First ferromagnetic layer 30: (Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(1.27),thickness 15 nm

First NiAl layer 40: thickness 0.21 nm

Non-magnetic layer 50: Ag, thickness 5 nm

Second NiAl layer 60: thickness 0.21 nm

Second ferromagnetic layer 70: (Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(1.27),thickness 5 nm

Cap layer 80: Ru layer, thickness 5 nm

The first underlayer 21 (MgO layer) was deposited by heating thesubstrate 10 to 500° C. and using a sputtering method. The substrate onwhich the first underlayer 21 was deposited was held at 500° C. for 15minutes and then allowed to be cooled to room temperature. Next, thesecond underlayer 22 (CoFe layer) was deposited on the first underlayer21 using a sputtering method. Next, the third underlayer 23 (Ag layer)was deposited on the second underlayer 22 using a sputtering method, andthereby the underlayers 20 were formed. The substrate 10 on which theunderlayers 20 were deposited was annealed at 300° C. for 15 minutes andthen allowed to be cooled to room temperature.

After allowing it to be cooled, the first ferromagnetic layer 30((Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(1.27)) was deposited on the underlayers20 formed on the substrate 10. The deposition of the first ferromagneticlayer 30 was performed by a co-sputtering method using a Co—Fe—Ga alloytarget and a Cu target as the targets.

The first NiAl layer 40 was deposited on the first ferromagnetic layer30 using a sputtering method. Next, the non-magnetic layer 50 (Ag layer)was deposited on the first NiAl layer 40 using a sputtering method.Next, the second NiAl layer 60 was deposited on the non-magnetic layer50 in the same manner as the first NiAl layer 40. Then, the secondferromagnetic layer 70 ((Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(1.27)) wasdeposited on the second NiAl layer 60 in the same manner as the firstferromagnetic layer 30. The substrate 10 on which the secondferromagnetic layer 70 was formed was annealed at 550° C. for 15minutes, and then allowed to be cooled to room temperature.

After allowing it to be cooled, the cap layer 80 (Ru layer) wasdeposited on the second ferromagnetic layer 70 formed on the substrate10 using a sputtering method. In this way, the magnetoresistance effectelement 101 illustrated in FIG. 1 was fabricated.

Further, thin film compositions of the first ferromagnetic layer 30 andthe second ferromagnetic layer 70 were obtained by performing an ICPemission spectroscopy for the ferromagnetic layer single film depositedon the silicon substrate, and then deposition conditions for desiredthin film compositions were determined.

A current was caused to flow in the lamination direction of thefabricated magnetoresistance effect element 101, and a current density(inversion current density) required to change a magnetization directionof the second ferromagnetic layer 70 was obtained. The change inmagnetization direction of the second ferromagnetic layer 70 wasascertained by monitoring a change in resistance value of themagnetoresistance effect element 101.

An MR ratio of the fabricated magnetoresistance effect element 101 wasalso measured. As for the MR ratio, a change in resistance value of themagnetoresistance effect element 101 was measured by monitoring avoltage applied to the magnetoresistance effect element 101 with avoltmeter while sweeping a magnetic field from the outside to themagnetoresistance effect element 101 in a state in which a constantcurrent is caused to flow in the lamination direction of themagnetoresistance effect element 101. A resistance value whenmagnetization directions of the first ferromagnetic layer 30 and thesecond ferromagnetic layer 70 are parallel and a resistance value whenmagnetization directions of the first ferromagnetic layer 30 and thesecond ferromagnetic layer 70 are antiparallel were measured, and the MRratio was calculated from the obtained resistance values using thefollowing expression. Measurement of the MR ratio was performed at 300K(room temperature).

MR ratio (%)=(R _(AP) −R _(P))/R_(P)×100

R_(P) is a resistance value when magnetization directions of the firstferromagnetic layer 30 and the second ferromagnetic layer 70 areparallel, and R is a resistance value when magnetization directions ofthe first ferromagnetic layer 30 and the second ferromagnetic layer 70are antiparallel.

Examples 2 to 5

Examples 2 to 5 are different from example 1 in that a substitutionelement that is substituted with the Co element is changed in the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example2, (Co_(0.9)Ru_(0.1))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example3, (Co_(0.9)Rh_(0.1))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example4, (Co_(0.9)Pd_(0.1))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example5, (Co_(0.9)Ag_(0.1))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70.

Examples 6 to 8

Examples 6 to 8 are different from example 1 in that a ratio of thesubstitution element that is substituted with the Co element is changedin the first ferromagnetic layer 30 and the second ferromagnetic layer70. In example 6, (Co_(0.8)Cu_(0.2))₂Fe_(1.03)Ga_(1.27) was used for thefirst ferromagnetic layer 30 and the second ferromagnetic layer 70. Inexample 7, (Co_(0.7)Cu_(0.3))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example8, (Co_(0.6)Cu_(0.4))₂Fe_(1.03)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70.

Examples 9 and 10

Examples 9 and 10 are different from example 1 in that a portion of theFe element is substituted in the first ferromagnetic layer 30 and thesecond ferromagnetic layer 70. In example 9,(Co_(0.9)Cu_(0.1))₂Fe_(0.93)Hf_(0.1)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example10, (Co_(0.9)Cu_(0.1))₂Fe_(0.93)Ta_(0.1)Ga_(1.27) was used for the firstferromagnetic layer 30 and the second ferromagnetic layer 70.

Examples 11 and 12

Examples 11 and 12 are different from example 1 in that a portion of theGa element is substituted with a different element in the firstferromagnetic layer 30 and the second ferromagnetic layer 70. In example11, (Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(0.41)Ge_(0.86) was used for thefirst ferromagnetic layer 30 and the second ferromagnetic layer 70. Inexample 12, (Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(0.41)Ge_(0.22)Mn_(0.64) wasused for the first ferromagnetic layer 30 and the second ferromagneticlayer 70.

Comparative example 1

Comparative example 1 is different from example 1 in that the Co elementis not substituted in the first ferromagnetic layer 30 and the secondferromagnetic layer 70. In comparative example 1,Co_(2.0)Fe_(1.03)Ga_(1.27) was used for the first ferromagnetic layer 30and the second ferromagnetic layer 70.

Comparative example 2

Comparative example 2 is different from example 1 in composition ratioof each element in the first ferromagnetic layer 30 and the secondferromagnetic layer 70. In comparative example 2,(Co_(0.9)Cu_(0.1))₂Fe_(1.0)Ga_(1.0) was used for the first ferromagneticlayer 30 and the second ferromagnetic layer 70.

Comparative example 3

Comparative example 3 is different from example 1 in that a compositionratio of each element is changed and the Co element is not substitutedin the first ferromagnetic layer 30 and the second ferromagnetic layer70. In comparative example 3, Co_(2.0)Fe_(1.0)Ga_(1.0) was used for thefirst ferromagnetic layer 30 and the second ferromagnetic layer 70.

The measurement results of inversion current densities and MR ratios ofexamples 1 to 12 and comparative examples 1 to 3 are shown in Table 1below. As shown in Table 1, all of the magnetoresistance effect elementsof examples 1 to 12 had lower inversion current densities compared tothe magnetoresistance effect elements of comparative examples 1 to 3.

TABLE 1 Inversion current MR density ratio Compositional formula (A/cm²)(%) Example 1 (Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(1.27) 2.5 × 10⁷ 12.3Example 2 (Co_(0.9)Ru_(0.1))₂Fe_(1.03)Ga_(1.27) 3.3 × 10⁷ 12.8 Example 3(Co_(0.9)Rh_(0.1))₂Fe_(1.03)Ga_(1.27) 3.6 × 10⁷ 11.7 Example 4(Co_(0.9)Pd_(0.1))₂Fe_(1.03)Ga_(1.27) 3.4 × 10⁷ 11.5 Example 5(Co_(0.9)Ag_(0.1))₂Fe_(1.03)Ga_(1.27) 2.4 × 10⁷ 11.9 Example 6(Co_(0.8)Cu_(0.2))₂Fe_(1.03)Ga_(1.27) 2.0 × 10⁷ 10.9 Example 7(Co_(0.7)Cu_(0.3))₂Fe_(1.03)Ga_(1.27) 1.6 × 10⁷ 10.6 Example 8(Co_(0.6)Cu_(0.4))₂Fe_(1.03)Ga_(1.27) 1.1 × 10⁷ 7.9 Example 9(Co_(0.9)Cu_(0.1))₂Fe_(0.93)Hf_(0.1)Ga_(1.27) 1.8 × 10⁷ 12.8 Example 10(Co_(0.9)Cu_(0.1))₂Fe_(0.93)Ta_(0.1)Ga_(1.27) 2.1 × 10⁷ 13.5 Example 11(Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(0.41)Ge_(0.86) 3.1 × 10⁷ 21.3 Example 12(Co_(0.9)Cu_(0.1))₂Fe_(1.03)Ga_(0.41)Ge_(0.22)Mn_(0.64) 3.1 × 10⁷ 22.4Comparative Co_(2.0)Fe_(1.03)Ga_(1.27) 4.2 × 10⁷ 12.3 example 1Comparative (Co_(0.9)Cu_(0.1))₂Fe_(1.0)Ga_(1.0) 4.0 × 10⁷ 7.7 example 2Comparative Co_(2.0)Fe_(1.0)Ga_(1.0) 5.2 × 10⁷ 8.6 example 3

EXPLANATION OF REFERENCES

101, 102, 103 Magnetoresistance effect element

10 Substrate

20 Underlayer

21 First underlayer

22 Second underlayer

23 Third underlayer

24 Fourth underlayer

30 First ferromagnetic layer

40 First NiAl layer

50 Non-magnetic layer

60 Second NiAl layer

70 Second ferromagnetic layer

80 Cap layer

201 Magnetic recording device

202, 203 Magnetic recording element

210 Magnetic head

220 Resistance measuring device

230 Power supply

240 Measurement unit

300 Spin current magnetization rotational element

400 Magnetic domain wall displacement type magnetic recording element

401 First ferromagnetic layer

402 Second ferromagnetic layer

403 Non-magnetic layer

404 First magnetization fixed layer

405 Second magnetization fixed layer

500 Magnetic strip device

510 Magnetic recording medium

511 Magnetic strip

511A First magnetic domain

511B Second magnetic domain

512 Underlayer

513 Substrate

520 Magnetic recording head

530 Pulse power supply

600 Magnetic domain wall movement type spatial light modulator

610 First magnetization fixed layer

620 Second magnetization fixed layer

630 Light modulation layer

631, 636 Overlapping region

632, 635 Initial magnetic domain region

633, 634 Magnetic domain change region

700 High-frequency device

701 Direct current (DC) power supply

702 Inductor

703 Capacitor

704 Output port

705, 706 Wiring

DW Magnetic domain wall

What is claimed is:
 1. A magnetoresistance effect element comprising: afirst ferromagnetic layer; a second ferromagnetic layer; and anon-magnetic layer positioned between the first ferromagnetic layer andthe second ferromagnetic layer, wherein at least one of the firstferromagnetic layer and the second ferromagnetic layer is a Heusleralloy in which a portion of elements of an alloy represented byCo₂Fe_(α)Z_(β) is substituted with a substitution element, in which Z isone or more elements selected from the group consisting of Mn, Cr, Al,Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α<β, and 0.5<α<1.9, and thesubstitution element is an element different from the Z element and hasa smaller magnetic moment than Co.
 2. The magnetoresistance effectelement according to claim 1, wherein the Heusler alloy is representedby the following general expression (1),(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)Z_(β)  (1) and in expression (1),X1 is the substitution element, Y1 is one or more second substitutionelements selected from the group consisting of elements having a smallermagnetic moment than Fe, and a and b satisfy 0<a<0.5 and b≥0.
 3. Themagnetoresistance effect element according to claim 2, wherein thesecond substitution element is one or more elements selected from thegroup consisting of elements having a melting point higher than that ofFe among elements of Groups 4 to
 10. 4. The magnetoresistance effectelement according to claim 1, wherein the Heusler alloy is representedby the following general expression (2),(Co_(1-a)X1_(a))₂Fe_(α)Z_(β)  (2) and in expression (2), X1 is thesubstitution element, and a satisfies 0<a <0.5.
 5. The magnetoresistanceeffect element according to claim 1, wherein the substitution element isone or more elements selected from the group consisting of Ni, Cu, Zn,Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au.
 6. The magnetoresistance effectelement according to claim 1, wherein the substitution element is one ormore elements selected from the group consisting of Cu, Ag, and Au. 7.The magnetoresistance effect element according to claim 1, wherein theHeusler alloy is represented by the following general expression (3),(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ga_(1-c)Z1_(c))_(β)  (3) and inexpression (3), X1 is the substitution element, Y1 is one or more secondsubstitution elements selected from the group consisting of elementshaving a smaller magnetic moment than Fe, Z1 is one or more elementsselected from the group consisting of Mn, Cr, Al, Si, Ge, and Sn, and0<a<0.5, b≥0, and 0.1≤β(1-c) are satisfied.
 8. The magnetoresistanceeffect element according to claim 7, wherein c in general expression (3)satisfies c>0.5.
 9. The magnetoresistance effect element according toclaim 1, wherein the Heusler alloy is represented by the followinggeneral expression (4),(Co_(1-a)X1_(a))₂(Fe_(1-b)Y1_(b))_(α)(Ge_(1-d)Z2_(d))_(β)  (4) and inexpression (4), X1 is the substitution element, Y1 is one or more secondsubstitution elements selected from the group consisting of elementshaving a smaller magnetic moment than Fe, Z2 is one or more elementsselected from the group consisting of Mn, Cr, Al, Si, Ga, and Sn, and0<a<0.5, b≥0, and 0.1≤β(1-d) are satisfied.
 10. The magnetoresistanceeffect element according to claim 9, wherein d in general expression (4)satisfies d<0.5.
 11. The magnetoresistance effect element according toclaim 9, wherein Z2 is Ga.
 12. The magnetoresistance effect elementaccording to claim 1, wherein α and β satisfy 2.3≤α+β<2.66.
 13. Themagnetoresistance effect element according to claim 1, wherein α and βsatisfy 2.45≤α+β<2.66.
 14. The magnetoresistance effect elementaccording to claim 1, wherein the non-magnetic layer contains Ag. 15.The magnetoresistance effect element according to claim 1, furthercomprising a NiAl layer containing a NiAl alloy between the firstferromagnetic layer and the non-magnetic layer and between the secondferromagnetic layer and the non-magnetic layer.
 16. Themagnetoresistance effect element according to claim 15, wherein athickness t of the NiAl layer is 0<t≤0.63 nm.
 17. A Heusler alloy inwhich a portion of elements of an alloy represented by Co₂Fe_(α)Z_(β) issubstituted with a substitution element, wherein Z is one or moreelements selected from the group consisting of Mn, Cr, Al, Si, Ga, Ge,and Sn, α and β satisfy 2.3≤α+β, α<β, and 0.5<α<1.9, and thesubstitution element is an element different from the Z element and hasa smaller magnetic moment than Co.